Kinematic and Numerical Studies on Stability Behavior of Two Himalayan Slopes from Uttarkashi, Uttarakhand

Landslides are one of the major natural hazards occurring in the mountainous areas. The Himalayan mountains are tectonically active. Due to the presence of highly weathered rock mass, folds and faults, frequent earthquake events, intense seasonal rainfalls, heightened anthropogenic activities such as road widening and construction of infrastructures, the Himalayan region is facing slope instability problems, and the situations are getting worse. One of the precursors to quantify the risks associated with the existing natural or already cut slopes is to carry out stability assessments prior to road widening activities. Several methods can be used to assess and analyze the stability of slopes and anticipate the probability of any impending landslides. For the present study, two slopes, one rock and the other one debris slope, located in the Garhwal Himalayan region of the Uttarkashi district, have been considered for kinematic analyses, and stability analysis using limit equilibrium method (LEM) and the finite element method (FEM) with the shear strength reduction (SSR) technique. In kinematic analysis, stereo-net plots of joint data collected for the studied rock slope have been prepared to determine the mode and direction of slope failure. The Mohr-Coulomb (M-C) criterion has been used for stability analysis of debris slope, while the generalized Hoek-Brown (GHB) criterion has been used for rock slope analysis. The stability assessment has been carried out for dry-static and wet-static conditions. A comparison has been made among the obtained factor of safety values. The stereo-net plot represents the formation of a potential wedge failure for the rock slope. The stability analysis revealed that the slope is partially to critically stable when dry but may become unstable under saturated conditions. Both the slopes are prone to failure during the monsoon season. Also, the factor of safety (FoS) values obtained from LE analysis are higher than those compared to the values obtained from FE analysis.